1. Field of the Invention
This invention relates to a magnetic head used in a magnetic recording/reproducing apparatus, such as a video tape recorder (VTR). More particularly, it relates to a magnetic head exhibiting abrasion characteristics equivalent to or higher than those in case of the crystal plane orientation of the .beta.-format, while making the best use of high output characteristics proper to the crystal plane orientation of the VHS format.
2. Description of the Related Art
Recently, technical innovation in the field of VTR in reducing its size and weight and in improving its recording density is outstanding, and attempts are made towards further increasing the recording density. These attempts may be typified by, for example, introduction of a double azimuth head and recording/reproduction by digital signals. For realizing these functions, circuit designing employing carrier signals of a frequency not less than 10 MHz is used for further narrowing the track width or the gap length of the magnetic head.
For assuring a playback output despite the tendency towards short wavelength and narrow track width, it is necessary to increase the relative velocity between the recording medium and the magnetic head further.
Thus, the magnetic head material is required to have superior abrasion resistance and high machining accuracy, such that single crystal ferrite or a crystalline guard material is widely employed.
In particular, in the case of the magnetic head formed of a single crystal ferrite material, crystal orientation of the single-crystal material is controlled for improving output characteristics and abrasion resistance. The reason is that, in the single crystal ferrite, magnetic anisotropy persists, such that the direction of easy magnetization or the direction of magnetic flux is varied appreciably with the crystal orientation, thus significantly influencing output characteristics of the single crystal ferrite magnetic head during recording/reproduction. On the other hand, the abrasion resistance of the single crystal ferrite depends appreciably on the crystal plane of the sliding surface of the recording medium and on the relation between the sliding direction of the recording medium and the crystal orientation.
For example, in the case of a single-crystal ferrite magnetic head for recording/reproduction by the VHS format, a crystal plane orientation, known as the J-type, in which the (211) plane, (111) plane or its vicinity and the (101) plane or its vicinity are arrayed for the sliding surface with the recording medium, the gap abutment surface and the plane perpendicular to the gap abutment surface, is extensively employed.
However, although the electro-magnetic conversion characteristics proper to the magnetic head in the case of the J-type crystal plane orientation are better than those of the .beta.-type crystal plane orientation, the sliding surface is inferior in abrasion resistance to those for the other crystal planes and, in addition, partial abrasion or the deviation in the top position of the sliding surface against the magnetic recording medium, referred to herein as R-top deviation, tends to be produced because of the tendency to differential abrasion by the sliding direction, as shown in FIGS. 1 and 2.
In the case of the VHS format, stringent demands have not been raised in connection with abrasion characteristics, as compared to the standards for Hi 8 magnetic material or .beta. formats, because of the broader abutment width of the magnetic tape and the lower relative velocity between the magnetic tape and the magnetic head. However, if the abutment width of the sliding surface against the recording medium or the depth length of the magnetic gap is diminished, as in Hi-8 format, or if the relative velocity between the recording medium and the magnetic head is extremely high, as n the case of the digital VTR, there is a risk that the abrasion leads to deteriorated durability or reliability of the magnetic head.